The present invention relates to a light-emitting device for use in various apparatuses such as image-taking apparatuses including a digital still camera and a video camera, and a camera-equipped cellular phone.
A typical illumination apparatus (light-emitting device) used in a camera is a flash unit which provides a large amount of illumination light by light emission in a flash discharge tube. In recent years, however, the large amount of illumination light, which has conventionally been used, is not necessarily required due to the increased sensitivity of an image-pickup device employing a CCD (charge-coupled device) sensor and a CMOS (complementary metal oxide semiconductor) sensor in an electronic camera. On the other hand, light-emitting diodes (hereinafter abbreviated as “LEDs”) have been improved in luminance and widely used for various types of illumination.
Thus, an illumination apparatus for taking images by using the LED as a light source has been proposed recently (see Japanese Patent Laid-Open No. 2000-89318). The illumination apparatus has a plurality of white LEDs arranged such that their light-emitters are located to face substantially the same direction close to each other, and an optical member disposed in front of the LEDs and including a plurality of integrally molded lenses associated with the respective LEDs.
A recent trend of electronic cameras is to have a capability to take an image at an extremely close range, for example, at several centimeters from an image-taking lens.
If the conventional illumination apparatus is used under the situation, illumination light having adequate characteristics cannot be provided especially in taking images at an extremely close range (macro photography). Specifically, part of the illumination light is blocked by an image-taking lens barrel to prevent uniform illumination all over the necessary irradiation area, and the extremely short distance to an object causes overexposure of the object to result in a failure to realize favorable exposure.
To prevent those problems, the macro photography often employs an illumination apparatus for macro photography which includes a ring-shaped light source for mounting around the end of an image-taking lens barrel. However, such an illumination apparatus tends to be large and expensive.
In this manner, it has conventionally been difficult for a small illumination apparatus to perform illumination appropriate for both of ordinary image-taking and macro photography. In reality, it is necessary to provide such an illumination apparatus which is suitable for both of ordinary image-taking and close-range image-taking and is also realized in a small size and low cost.
For example, Japanese Patent Laid-Open No. 2001-255574 has proposed an illumination apparatus which has a ring portion for mounting around an image-taking lens barrel of a camera. The illumination apparatus directs light from a light source toward the circumference direction of the ring portion and causes the light reflected by a reflecting surface of the ring portion to emerge from an emergence surface opposite to the reflecting surface. This apparatus enables the light from the single light source to be irradiated in ring shape from around the image-taking lens barrel.
As described above, the luminance of the LED has been increased recently. However, as shown in Japanese Patent Laid-Open No. 2000-89318, a sufficient light amount for taking images is difficult to provide unless a plurality of LEDs are used.
The illumination apparatus proposed in Japanese Patent Laid-Open No. 2001-255574 directs the light from the single flash discharge tube (xenon tube) toward the ring portion disposed around the image-taking lens barrel. The apparatus cannot be used without any change when a plurality of LEDs are used as light sources. In other words, no proposal has been made conventionally of an illumination apparatus which allows efficient irradiation of light from a plurality of LEDs to realize an illumination (light distribution) characteristic suitable for macro photography and also has a small size.